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Full text of "The Melon Aphis"



Historic, arcJiived document 

Do not assume content reflects current 
scientific l<nowledge, policies, or practices 



Circular No. 80. 



United States Department of Agriculture, 

BUREAU OF ENTOMOLOGY, 

L. O. HOWARD, Entomologist and Chief of Bureau. 



THE MELON APHIS. 

( Aphis gossy2)li Glov. ) 

By F. H. Chittenden, 

Entomologist in Charge of Breeding Experiments. 

NATURE OF ATTACK. 

The melon aphis, or, as it is commonly known, the ''melon louse," 
injures plants hy piercing them with its beak and sapping their vital- 
it3^ It occurs from early spring to late in autumn on melons and 
other cucurbits of all kinds, and on many other crop plants, and in 
seasons which favor its increase, notabl}" in summers following springs 
that are cool and rain}^, it frequently develops in enormous numbers 
and does verj^ serious damage, collecting in masses on the under sur- 
face of the leaves of plants and causing them to curl, shrivel, and lose 
color, and interfering with the ultimate development of the fruit. 
Often it kills plants outright, and destroys whole fields or greatly 
reduces the 34eld of fruit. An affected cantaloupe plant is illustrated 
b}^ figure 1. 

The melon aphis, like others of its kind, excretes ''honey dew," but 
this is not so copious as in the case of many species of aphides, for 
example, certain forms which affect trees. When, however, the aphis 
under discussion becomes unusually abundant, the honey dew covers 
the leaves of the affected plants with a thin, sticky coating on which 
the white cast skins of the aphides adhere, and this attracts attention 
to injury, as does also the wilting and dying down of the plants. 
Some persons notice this honey dew, and are unaware of the presence 
of the insects. They speak of the injury as "hone}^ dew," and have 
even applied this name to the insect itself." 

Quite too frequently, b}^ the time the presence of the melon aphis 
in injurious numbers is noticed, irreparable damage has been accom- 
plished and the insects have for the most part migrated to other 
pastures. 

« Attack by many forms of aphides, especially those which excrete honey dew 
more copiously, can be readily detected hy the presence of insects which feed on the 
sweet excretion. Among these are flies, wasps, bees, and especially ants. The 
melon aphis, however, is not an especial favorite with ants, altho some common spe- 
cies are occasionally found in attendance upon it. The pavement ant ( Tetramorium 
cxspitiun L. ) is the only species which has thus far been observed by the writer, and 
neither ant nor aphis appears to be in any way dependent on the other for its exist- 
ence, contrary to that which is the case with many other aphides, particularly those; 
which have root-feeding forms. 

10248— No. 80—06 



DESCRIPTIOX. 



The melon apliis is a minute, soft-bodied creature, of variable color, 
usuall}^ of some shade of green or greenish black: in its young and 
wingless stages, louselike in appearance; and of sluggish habit thru- 
out its existence. The general appearance of this species in its most 
commonly observable stages is indicated in figure 2, highl}- magnitied. 
A brief description of the stages figured will suffice for the present 

purpose. 



The egg has been 
described by Mx. Th. 
Pergande^' as of regu- 
larly oval shape and 
measuring about 0, 6'""' 
in length; 3'ellowish 
or greenish when first 
deposited, soon chang- 
ing to jet black. 

The larval aphis or 
nymph (fig. 2, 7j) when 
first born or hatched 
presents no observable 
characters for com- 
parative description. 
It measures less than 
0.5'""' and is pale in 
' color, turning later 
to yellow. The last 
nymphal stage, corre- 
sponding to the pupa 
of other insects, is 
sufficiently illustrated 
at c that it requires 
no verbal description. 
The apterous or wing 
less female, which is 
viviparous ( g i v i n g 
birth to living j^oung), 
is figured at d. Great 
variation is exhibited in this stage, from pale yellow to very dark green, 
with black nectaries or honey tubes and pale whitish-yellow legs and 
antennae This stage varies in length from 1.5 to 1.8""". The winged 
female is illustrated at «, which shows a form with pale abdomen. 
The body is more slender than in the wingless form, the length being 

« Insect Life, Vol. VII, pp. 309-315, 1895. Technical descriptions are furnished 
also by Forbes, 12th Kept. St. Knt. Til. f. 1882 (1883), pp. 83-91. 




Fi(.i. 1.— Cantaloupe leaves showing curling caused by melon aphis 
aphides on lower surface. Slightly reduced (original) . 



from 1.2 to 1.8""", while the wings expand from -1.5 to 6"^™. A darker 
form of the female is shown in profile at ah^ and the antenna, much 
enlarged, at aa. The male has not as vet been recognized. 

This is by far the most important and abundant aphis affecting- 
melons and other cucurbits, and is not likel}^ to be confused with any 
other species occurring habitually on the same class of plants." It is, 
indeed, a ver}^ important pest, and, taken season after season, the worst 
aphis occurring in this countr3\ 




Fig. 2.— Melon aphis {Aphis gossypii): a, winged female; aa, enlarged antenna of same; ab, dark 
female, side view, sucking juice from surface of leaf; b, young nymph or larva; c, last stage of 
nymph; d, wingless female. All greatly enlarged (author's illustration). 



DISTRIBUTION. 

The origin of the melon aphis is doubtful, but is probabh- tropical, 
since this insect shows a decided preference for plants of a tropical 
nature, such as the cucurbits, cotton, and orange. Southward the 
aphis occurs in the West Indies, in Mexico, and in Brazil, and doubt- 
less elsewhere in South America. It is very generally distributed 
thruout the L^nited States, but does more injury in the southwest than 
elsewhere. In Texas, Kansas, and Nebraska it is particularly trouble- 
some to melons, and in the last two States to cucumbers, which are 
there extensively grown for pickling. But it msij at any time create 

«The squash aphis {Nectarophora ISiphonophora] cucurhitx Middleton), a much 
larger species, more uniformly green, and of a much lighter and brighter color, is 
often found on cucurbits, but seldom in sufficient numbers to cause noticeable 
damage. 



more or less trouble in northern regions, particularh^ in Virginia, 
Maryland, Delaware, and New Jerse}- , where cucurbits are much cul- 
tivated. Occasionally it is injurious as far north as Minnesota and 
w^est to California. It has been collected also in Adelaide. South 
Australia. 

INSTANCES OF INJURT. 

The melon aphis first attracted notice thru its injuries to cotton in 
1854, and from that time on it has done more or less damage 3^ear by 
year, and, in view of its rapacity, rapid multiplication, and omnivo- 
rous habits, will no doubt continue injurious in spite of all that can 
be done to repress it. As a melon and cucumber pest it was noticed 
in Florida and southern Illinois in 1880, and in the next three years 
caused considerable losses in those States and in Georgia. Soon after- 
wards it became recognized as a strawberr}^ pest. In later ^^ears many 
other food plants were added to its known dietary. The years 1892, 
1893, and 1898 were unusually bad "aphis years." 

In 1893 information was received from a pickle company of Omaha, 
Nebr., of severe injury in that State. This company was growing 
between 30,000 and 50,000 bushels of cucumbers a .year, and sev- 
eral hundred neighboring farmers grew this vegetable for the com- 
pany. Two-thirds of the crop grown in 1892 was destroyed by the 
aphis, and in 1893 half of the crop was lost. These injuries made it 
diflicult to induce outside planters to grow for the company. 

In 1898 this species was extremely troublesome. In order that a 
good idea of its destructiveness may be had^ some reports are cited. 
In January injury was reported on cucumbers in Florida and in Maj^ 
to strawberries in Delaware, where the insects were described as 
"taking everything clean." By June this insect had been very 
injurious to watermelon in southern Texas, when it destroyed many 
acres of earl}^ vines. In July Texas correspondents reported the 
destruction of 1,000 acres of cantaloupes in one locality, and the out- 
break assumed such proportions as to cause much newspaper com- 
ment. One company reported that the ravages of this pest had cost 
them $20,000, and that agriculturists of that section had sustained irre- 
trievable loss. In November a Pennsylvania correspondent reported 
losses to cucumbers grown under glass, and in December this aphis 
resumed its ravages to cucumbers in Florida. 

LIST OF FOOD PLANTS. 

The insect here considered is the most nearly omnivorovis of any 
known species of aphis. The list of plants upon which it has actually 
been found feeding shows great diversity, and future observations 
may add many more host plants. 

It is partial to the plants that have previoush^ been mentioned — 
melons and other cucurbits, cotton, okra, orange and other citrus 



fruits, strawbeiT}^, and purslane — but it attacks also clover, beans, 
beets, spinach, tomato, hops, and pear, and several ornamental plants, 
including' hydrangea, begonia, ground ivy {Nepeta glechoma)^ Aca- 
lypha, and morning-glor}'. From its abundance on some of these 
plants it has received a number of common as well as Latin synonym- 
ical names, the former including cotton aphis, orange aphis, cucumber 
louse, and cantaloupe louse/^ It is frequently called also the "black 
aphis," especially in its occurrence in greenhouses. Mr. Pergande has 
found it feeding upon a large number of weeds, among which are shep- 
herd's purse, pepper-grass, pigweed (Amaranth us), dock (Rumex), bur- 
dock (Arctium), dandelion, lambsquarters (Chenopodium), plantain, 
chickweed, button-weed (Diodia), mallow, dogwood (Cornus), and 
Jamestown or jimson weed (Datura). 

Since these aphides are not at all particular as to their food, when 
they migrate from their favorite plants they start colonies on nearly 
any plant that chances to be in their line of flight. The writer has 
seen asparagus and violet attacked, the latter grown in greenhouses. 

LIFE HISTORY. 

Attack to cultivated plants begins from early spring till consider- 
abl}^ later, and is made by winged individuals fl3^ing from weeds which 
serve as alternate food plants. Infestation naturally commences earlier 
in the South than northward, and may be simultaneous with the appear- 
ance of the crop above ground. Soon after the plants have developed 
leaves a few winged aphides can usually be found, and these are the 
forerunners of myriads to follow. As often as a plant becomes 
exhausted of its vital juices by the sucking mouth-parts of innumera- 
ble aphides, winged individuals are developed which migrate to other 
plants, so that migration in the case of this species is carried on prac- 
tically thruout the season. Flight from one kind of food plant to 
another, or from one field to another, is caused also by disturbance 
from the abundant natural enemies of the insect. The great num- 
bers of this species sometimes suddenly discovered on melons, cotton, 
orange, and. other plants are often due to enforced migration on account 
of the death of other food plants in the vicinity, such as might be 
caused by atmospheric conditions, or by the ravages of the aphides 
themselves, or of other insects. The removal of the crop on which 
the insect was at work will produce the same efi'ect. 

NATURAL ENEMIES. 

There is perhaps no better example, among insects, of a common 
and widespread species being held in abeyance and limited to innoxious 

« The synonyms include Aphis {Siphonophora) citrifolii Ashm., ApMs citrulli Ashm., 
Aphis cucumeris Forbes, Aphis forbesi Weed. It is still mentioned in literature as 
A. cucumeris. 



6 

numbers (save in exceptional seasons) b}^ natural enemies than the 
melon aphis. The usefulness of these natural enemies, of which a 
large number have been recorded, in subduing the aphides can not be 
overestimated. Garden and field aphides generall}^ are subject to 
attack by the same classes of parasitic and predaceous enemies. The 
number of species of insects known to prey upon the melon aphis is 
about 35. The list includes many ladybirds or " lad3^bugs " (Cocci- 
nellidae)," which destroy the aphis both as beetles and as larvse; the 
maggots of certain syrphus-flies (Syrphidse),^ which consume large 
numbers of aphides; aphis lions — the larvae of lace-wing flies, of the 
families Chrysopidse and Hemerobiid^e.^ A number of species of para- 
sitic insects, chiefly minute forms of Braconidse, are also ver}^ impor- 
tant checks on the increase of aphides.^^ Many, too, are destroj^ed by 
parasitic fungi. 

The insect enemies of these, as of other aphides, keep their hosts, 
in many portions of the country and in ordinary seasons, in nearly 
complete subjection. The parasites, in particular, are most effective 
in dr}^, warm weather. In cooler, moist summer weather, especiall}^ 
following the same atmosvherlc conditions in spi'ing^ when vegetables 
subject to aphis injury are starting growth, these otherwise natural 
checks are less active, and the aphides, as a result, frequently gain the 
ascendency. 

Some of the commonest species of ladybird enemies of this and 
other aphides are illustrated in figure 3. In the ^' aphis j^ear" of 1898 
the Scymnus (fig. 3, A, ^', j) was particularly abundant in and near the 
District of Columbia on aphis-affected plants. ' A still more abundant 
and useful form of this class of insects is the convergent ladybird 
{Hipjjodamia convergens Guer.), shown in fig. 3, «, ^, c. It is fre- 

^Hippodamia convergens Guer. and Cydoneda sanguinea L. are prominent enemies, 
as are also Megilla maculata De G. (fig. 3, d, e) and Cocdnella 9-)iotata Hbst. Other 
species are Scymnus terminatus Say, S. caudalis Lee, S. cervicalis Muls. (A), 
Chilocorus bivulnerus Muls., Exochomus constristatus Muls. (H), and Hippodamia 
13-punctata L. 

^Syrphus flies include /S^rp/ms americanMs Wied., Allograpta obliqua Say, Baccha 
clavata Fab. {babista Walk.), B. lugens Loew. (H), B. cognata Loew. (H), B. fusci- 
pennis Say (A), and Eupeodes volucris 0. S. An agromyzid fly, Leucupis nigricornh 
Egger, also preys on this aphis. Cecidomyiid enemies include certain undetermined 
species of Contarinia (Diplosis). 

<^ Among the lace- wing flies are Chrysopa oculata Say, C. plorabunda Fitch, C. albi- 
cornis Fitch (A), C. nigricornis Burm. (A), C. lineaticornis Fitch (A), C. attenuaia 
Walk. (A), Micromus posticus Walk., and Hemerobius gossypii Ashm. (A). 

^ Parasitic braconids include Trioxys testaceipes Cress. , Lysiphlebus gossypii Ashm., 
L. citraphis Ashm., L. cucurbitaphis Ashm., L. minidus Ashm., Lysiphlebus sp., and 
Pachyneuron sp. A chalcis fly, Stenomesius aphidicola Ashm., has also been reared. 

The species followed by ( H) were observed attacking Aphis gossypii on orange trees 
in Florida by H. G. Hubbard, those marked (A) by Wm. H. Ashmead on cotton in 
Mississippi. The others are mostly well known, and have been observed by various 
persons, as well as by the writer. 



quently mistaken for tlie parent of the aphides. Another very efficient 
enem}'. the nine- spotted ladybird, is shown in tig-ure 3./', q. 

One of the most abundant syrphus-% enemies is illustrated by 
lig'ure 4. 










Fig. 3.— a. Adult of convergent ladybird {Rippodamia convergent); b, pupa of same; c, larva of same; 
d. adult of spotted ladybird {Megilla maculata) ; e, larva of same; /, adult of nine-spotted ladybird 
{Coccinella 9-notata); g, larva o-f same; h, adult of Scyiniius terminatus; i, larva of same; j, pupa of 
same. All enlarged: size indicated by hair line at right (author's illustrations, f-j original). 

Of the natural enemies which have been enumerated, ladj^birds are 
particularh^ valuable, owing principallv to the fact that they are active 
at all seasons, especially at the outset of aphis attack. Parasites are 
most effective toward the end of the season, when thev often reduce 



8 



the aphides so that few are left to hibernate and produce other gen- 
erations of the pest the following- 3^ear. 

The value of these natural enemies against aphides is such that 
entomologists frequently advise the employment of remedies onl}^ 
when the enemies are not present in abundance. The possible utiliza- 
tion of natural enemies in the field will be considered on pages 15 and 
16 of this circular. In tobacco fumigation, which will -presently be 
considered, we have an almost ideal remed}^ for the reason that, while 
aphides are all destro3^ed, a considerable- proportion of the ladybirds 
and other hardy beneficial insects, which are practicallj^ always present 
on the infested vines, survive this treatment. 




Fig. 4. — A syrphus-fly {Syrphus ribesii): a, fly; b, lateral view of head; c, larva or active immature 
form; d, anal spiracles; e. thoracic spiracle of same. All much enlarged (original). 

METHODS OF CONTROL. 

The severe losses occasioned by the melon aphis in its seasons of 
greatest destructiveness could be largely mitigated and in many cases 
almost entirel}^ prevented if the employment of methods for its con- 
trol were begun uj?o?i the insecfs first apj^ecirance. For its successful 
treatment it is necessary to keep constantly in mind several of the 
facts that have already been given more in detail. In ordinary sea- 
sons the species is controlled by the combined operation of natural 
elements and insect enemies, but at times when the weather is unfa- 
vorable to the development of these enemies the grower should be on 
the alert. The presence of the aphides is often not detected until they 
are numerous, and even then they are not apt to be noticed unless the 
loirer surface of the leaves be examined. 

All things considered, the most satisfactory way of controlling this 
insect is b}^ fumigation. As an aid, however, cultural methods are 
necessary. In the kSouth spraying with kerosene and other emulsions 
is preferred to the bisulfid of carbon method, and tobacco is now much 
used, especially in Texas. The encouragement of natural enemies 
gives promise of success. 



I 



BISULFID OF CARBON FUMIGATION. 

This treatnient of the melon aphis has been used successfully for 
some time, and is valuable in small fields, but less profitable where 
cucurbit or other crops are grown over large areas. It consists in 
evaporating bisultid of carbon under tubs, or similar tight receptacles, 
such as pails, buckets, or boxes. The chemical is employed at the 
rate of a dram (about a teaspoonful) to each cubic foot of space: a 
tablespoonful will serve for ordinary small tubs. This method of 
treating the plant does not injure it, and if the tub fit tightly to the 
ground, so as to retain the vapor of the bisulfid, all of the aphides 
which are covered will be killed. This method may be followed suc- 
cessfully in large fields if the grower be careful to watch the vines for 
the first appearance of the insects, and to treat such hills as require 
fumigation, removing and destroying plants that are badly afi^ected to 
prevent the spreading of the insects to others.^ 

Cautiox. — In the use of bisulfid of carbon as a fumigant for aphides 
the usual precaution should be observed not to expose the fumes to fire. 
The operators must not smoke during this process! As the gas is 
heavier than air there is no danger, if ordinary care is observed, that 
the fumes will be inhaled b}^ human beings. 

HYDROCYANIC-ACID GAS TREATMENT. 

This gas, as has been demonstrated by Prof. E. D. Sanderson, can 
be used in the field in much the same manner as the bisulfid of car- 
bon, with wooden tubs or buckets. It has not, however, been adopted 
b}^ growers and we do not recommend it. It possesses an advantage 
over bisulfid of carbon in that the cover used in gassing need not fit 
closely to the earth. On the other hand, it is decidedly more danger- 
ous to human life and must therefore he handled ivith the greatest care! 

As a greenhouse insecticide this gas is a perfect remedy for aphides 
and other small and soft-bodied insects. It is used where tobacco is 
unsafe; for example, in violet houses, violets being especially subject 
to '^spof after fumigation with tobacco. The method of applying 
hj^drocyanie-acid gas is described in Circular No. 37 of this Office. 

PYRETHRL'M POWDER. 

Pyrethrum or buhach insect powder, administered divy with a pow- 
der bellows to the lower surface of leaves, will kill the insects, altho 
these sometimes do not appear to be affected at first. A second or 
third application is sometimes necessary. This is an expensive rem- 
edy and can not be used with profit on large fields or on plants with 
large leaves, like squash. 



^' In New Jersey and Colorado many growers simply take out and bury such badly 
infested plants as are noticed when the hills are turned for cultivation. 



10 



FUMIGATION WITH TOBACCO PREPARATIONS. 



Tobacco extracts and fumigating powders iiave been extensively 
used for a number of years by ilorists as fumigants against aphides 
and other insects occurring in greenhouses, such as white %, thrips, 
and other small, delicate, and soft-bodied insects. The extracts con- 
tain a larger proportion of nicotine than ordinary decoctions prepared 
by steaming waste stems and powdered tobacco, and are therefore 
much more effective, which is true also of the powdered fornis of nico- 
tine. A number of these preparations are on the market and are 
advertised in the principal florists' journals and in other agricultural 
periodicals. They are used in various ways, and directions are fur- 
nished with the packages purchased. The liquid preparations vary in 
strength from 35 or -iO per cent up to 80 to 85 per cent nicotine. 

FIELD FUMIGATION WITH TOBACCO. 

During the years 1904 to 1906 the employment of tobacco or nico- 
tine preparations in destroying the melon aphis in the field was the 
subject of experiment in Texas b\^ Messrs C. E. Sanborn and E. D. 
Sanderson." These have stated to the writer that, judging from their 
experimental use of this method and its practical use b}^ extensive 
growers, it bids fair to become the best method of dealing with the 
melon aphis in its occurrence in the South. The process is in brief 
the fumigation of a dry preparation under a cloth-covered frame 
placed over the affected vines. In 1905 and 1906 the writer found 
that a very short exposure to tobacco fumes killed aphides, when other 
insects, such as thrips, survived a considerably^ longer treatment. 

In practising this method Mr. Sanborn has used apparatus substan- 
tiall}' as follows: 

Preparation of the frame and cover. — For vines 2 or 3 feet long he 
advises a light frame tt by 6 feet, supported by legs 8 inches in length. 
Lumber three-fourths inch thick and 2 inches wide is suitable. 
Strengthen the frames by connecting the ends with acrosspiece. Two 
diagonals are also used for strengthening the frame and for conven- 
ience in handling, the latter being attached after the cloth cover is in 
position. The cover is of muslin of a cheap grade (7 or 8 cents a 
yard) and sufficiently compact to prevent a passage of gas thru its 
meshes after being oiled. Its size should be about 2 feet wider and 
2 feet longer than the frame which it covers. This is sufficient for an 
8-inch wall and a 4-inch lap to the ground. Dirt is placed about the 
bottom to keep the gas from escaping there. 

After the cloth has been cut and sewed into the sizes desired it is 
saturated in a vessel of linseed oil which fills the pores. It is then 

« An experiment with tobacco smoke as a remedy for this species was made by 
Dr. S. A. Forbes in 1882. The result was not a perfect success, for the reason that a 
bee smoker was used and the smoke was blown under canvas hay caps covering the 
affected plants. Nevertheless from 50 to 75 per cent of the aphides were killed by 
10 minutes' exposure. 



11 

wrung out, slightly dried, and placed over the frame and held in place 
by nailing the diagonals to the frame above the cloth. A gallon of 
linseed oil is sufficient for rendering four covers of the size above 
specified sufficient!}^ air-tight for this method. 

The number of frames for use depends upon the degree of infesta- 
tion and the rapiditj^ of the operators. Ordinarily about 10 frames 
are sufficient for one man's attention. 

Method of application. — The frame is placed over the infested plant. 
One sheet of the fumigating preparation is torn into from two to four 
or more equal parts (according to directions on the package or j^s 
experience may decide) and each part is put in a tin fruit can under 
the frame near a corner and then ignited. The cans are perforated 
at the bottom by driving a large nail in at the side. It is well to use a 
long taper or fuse for lighting the f umigant. afi'ording the more active 
beneficial insects time to escape from under the cover before the tobacco 
fumes are given ofi". Earth is then heaped on the border of the' cloth 
on the ground to prevent the escape of the smoke. The frame should 
remain in position ten or fifteen minutes, or longer if preferred. Each 
operator should have enough frames to handle so that each frame in 
succession ma}^ remain on a vine during the time mentioned. 
. In localities where the aphis is most injurious local merchants who 
deal in insecticides should be informed of the fact and requested to 
keep a supply of fumigating preparation always in stock. 

The best time for fumigating is when there is no wind and the vines 
are damp. In moderately dry weather, however, good results may 
be ol:>tained. 

Cautiox. — Care should be exercised not to allow the dry fumigant 
to ignite. It should smolder only. Vines should not be disarranged 
except where the}' protrude a few inches beneath the cover. The 
leaves should not touch the top of the cover. 

Yariations of the fumigating frame. — The frame described above 
has been used in the fumigation of young plants in southern Texas. 
The size and make-up of the frames may be altered or improved by the 
individual grower to adapt them to the size of the vines and the nature 
of the plant to be fumigated. Farther north than Texas manifestation 
of injury is not usually observable until the plants have made consid- 
erably larger growth, and a larger frame, say about a foot high, will 
be found more desirable for general use. Unbleached cotton of com- 
pact mesh, at 10 cents a yard, answered as well as the oiled "muslin" 
in experiments conducted by the writer, and there is a saving of time 
in its use. Moreover, it does not collect dirt nor soil the clothing and 
other objects with which it comes in contact. 

For the treatment of plants other than cucurbits, such as cabbage 
aflected by the cabbage aphis, eggplant, tomatoes, and other truck 
Mr. Sanborn advises a hood, using a frame made of two wires bent in 
a semicircle. Strong barrel hoops may be substituted, and the cover 
tacked to them at the top where they cross and at the bottom of the 



12 

hoops. Ornamental plants of low-growing sorts ma}^ be fumigated by 
means of such a hood, while for moderately high plants, such as roses, 
which are much affected by two common species of aphides, special 
covers ma}^ be constructed. 

VAPORIZING AND FUMIGATING TOBACCO IN GREENHOUSES. 

In the vaporization of tobacco — a practise which has been in use 
since about 1894 and which has largely superseded ordinary dr3^-tobacco 
fumigation in many sections^tobacco stems or dried tobacco, in one or 
another of its various proprietary forms, are placed in a kettle, metal 
pail, or similar receptacle. A hose is then connected with a steam 
pipe, the nozzle inserted in the receptacle, and the house to be treated 
becomes saturated with the vapor of tobacco, with the resulting 
destruction of aphides and other soft-bodied insects that may be pres- 
ent, such as thrips or "white fly." 

Liquid preparations are more generally evaporated over alcohol or 
other lamps, or are placed upon steam pipes, or hot irons are put into 
the receptacles. For general greenhouse fumigation, fumigating 
powders are placed in shallow pans, and a few drops of kerosene are 
added to facilitate ignition. The dry fumigant is designed to burn 
slowl}', so as to produce a smudge which, when dense, is fatal to 
aphides. This process of treatment may be applied at any time, by 
day or over night, and upon its completion the house is ventilated. In 
some cases the plants are syringed, but this is not necessary with plants 
like cucumbers. A surplus of moisture is to be avoided, owing to the 
liability of inducing ''spot," mildew, and other fungous diseases on 
plants susceptible to such maladies. 

The amount of a tobacco compound to be used depends upon its 
strength, the plants to be treated, and the size of the greenhouse. Sev- 
eral forms are for sale under different trade names. It is not probable 
that these differ greatly from one another in value, but there is much dif- 
ference in their strength. They are put up in both dry and liquid forms. 

In experiments conducted on greenhouse cucumbers at the Massa- 
chusetts Agricultural Experiment Station, at Amherst, one of these 
preparations has been used successfully at the rate of 5 or 6 teaspoon- 
fuls to li pints of water, and vaporized in a space of about 5,000 cubic 
feet. The length of exposure in this case was over night. Thus used, 
it does not injure delicate plants, like cucumber, but it kills all aphides 
and nearly all thrips — for which it was used primarih^ and which are 
not infrequently associated with aphides on the plants to be treated." 

"Thrips and "white fly" {Aleyrodes spp. ) are more resistant to poisonous gases 
than are aphides. The former are most effectively destroyed while in the soft imma- 
ture stages. The adult thrips are hardier and, being winged and more active, spring 
and fly away, and are thus not so easily brought in direct contact with insecticides 
like' kerosene emulsion. The white flies, on the other hand, are more susceptible 
to poisons while in the active adult stage. The nymphs are of firmer consistency 
and comparatively resistant. Remedies for the greenhouse white fly are discust in 
Circular No. 57. 



13 

Tohacco in fine powder form dusted lightly on very young- plants 
serves both as a repellent and as a mulch, or fertilizer. It is claimed 
by some to deter the striped cucumber beetle; others report that it is 
not effective for this beetle. 

A successful fumigation or vaporization of a cucumber house 
infested with the melon aphis was made also in elune, 1906, at Ana- 
costia, D. C. A different preparation was used, and 66,000 cubic feet 
of greenhouse space was fumigated, 22 ounces of the liquid, or 1 ounce 
to 3,000 cubic feet, being employed. The work was under the writer's 
direction and conducted b}- Mr. I. J. Condit, with the cooperation of 
Mr. J. W. Bryan, owner of the house. At the end of an hour and 
fifteen minutes, when the ventilators were opened and the greenhouse 
aired, the aphides were found dead and d^dng, and the cucumbers 
were unharmed. Eight evaporators were used in this instance, each 
holding a little less than 3 ounces of the liquid. It is quite probable 
that a considerabl}^ smaller amount of the preparation, sa}^ 1 ounce to 
5,000 cubic feet, with an all-night exposure, would have accomplished 
the same object. The cost of fumigation is not above $2.50 for a 
house containing 64,000 cubic feet. 

Caution. — Before fumigating an entire greenhouse with any sub- 
stance a preliminary test is always advisable to guard against acci- 
dents and to avoid Avaste of material. In the case of one liquid 
tobacco fumigant used at Washington, the preliminary test showed 
that, employed at the strength advised by the manufacturers (/. e., 
without dilution), it ignited in the evaporating pan instead of vaporiz- 
ing. This trouble was obviated b}^ diluting the fumigant with half its 
amount of water, the further precaution being taken of placing a wire 
gauze beneath the pan and over the flame. In the case of some alcohol 
lamps used for this purpose the flame is apt to be too strong, espe- 
cially if placed too near the evaporator. This causes the glass to break. 
Brass or other metal lamps are therefore preferable. Unless the 
lamps and wicks are of good quality and fit properly, the alcohol is 
apt to ooze out around the cork and burn on the sides of the lamp and 
thus, also, cause breakage. 

As a general rule it is best not to fumigate in hriglit sunlight, and 
not when delicate foliage or flowers have globules of water on them. 

.SPRAYING METHODS. 

Kerosene emulsion and soap solutions. — The melon aphis could be 
much more readih^ dealt with if it were not for its unfortunate habit of 
feeding on the under surface of leaves — which are often badly curled, 
as shown in figure 1 — and for the further fact that in large fields, par- 
ticularly late in the season when the leaves are large, the vines grow 
so closely together, frequentlv becoming interlaced, that spraying by 
ordinary means is impracticable. Underspraying is an absolute neces- 
sity, and a sprayer should be used fitted with an upturned elbow and a 



14 

nozzle of the Vermorel type to secure this effect. An elbow designed 
for this purpose is shown in figure 5. 

Kerosene-soap emulsion, the standard remedy for aphides, is the best 
insecticide for spraying purposes, but various soap solutions are used 
both for the melon and pea aphides. The}^ are diluted with 6 to 8 parts 
of water. The emulsion and soap washes are of particular value when 
the plants are small, as then the aphides can be more readily reached 
than when the leaves have grown to larger size; and, to repeat, if inju- 
ries are to be averted the insect should be checked on its first appear- 
ance, not alone on cucumbers, melons, squashes, or whatever the main 
crop may be, but upon all neighboring plants which may harboi the 
insect, including beds of strawberry or groves of orange trees. 

Kerosene- soap emulsion is prepared by combining 2 gallons of kero- 
sene, one-half pound of whale-oil soap, or 1 quart of soft soap, with 1 
gallon of water. The soap is dissolved in boiling water and then 
poured while still boiling hot (away from the fire) into the kerosene. 
The mixture is then churned rapidly for about five minutes, pumping 
the liquid back upon itself by means of a force pump and direct-dis- 
charge nozzle throwing a strong stream. At the 
end of this time the mixture will have become of 
the consistency of thick cream. Properly prepared, 
an emulsion will keep almost indefinitel}", and 
should be diluted onh^ as needed for use. For 
most species of aphides the staple emulsion should 
-, ^ ^^^ ,, , be diluted with from 10 to 20 parts of water. In 

Fig. 5.— Elbow attach- -i 

ment for underspray- the preparation of kcroscnc femulsion a force pump 
mg. Reduced. ^^ ^ necessit}^ siucc if not made according to 

directions a perfect emulsion is not formed. There is then danger of 
injury to the plants bv the kerosene, as also useless waste. There is 
danger and waste, too, if the insecticide is not applied by means of a 
fine nozzle in the form of a spray^ which should be fin-e and mist-like, 
or "like a fog," as some one has aptly exprest it. It should be 
spra3^ed onl}" for a long enough time to cover the plants, otherwise 
the liquid forms into globules and runs ofi'. Figure 6 illustrates 
the method of operating a knapsack spraj^er so as to produce an 
underspraying. 

Spraying vnth u:ater. — Where a few plants only are to be protected, 
and it is possible to direct a strong stream of water upon them from a 
garden hose, syringe, or spraying machine, so as to wash ofi* the 
insects, the aphis can be materially checked without the use of other 
materials. Such of the insects as come into direct contact with a stift' 
spra}^ are unable to survive, while others that are dislodged from the 
plants do not succeed in returning. Many are wingless during the 
greater part of the season and unable to crawl any distance, particu- 
larly if the ground be dry and hot. 




15 



CULTURAL METHODS. 



Cultural methods give greatest promise as remedies. Clean garden- 
ing or farming with fall plowing should alwaj^s be followed, as these 
form a most valuable measure of prevention of injury b}^ this and 
other insects that are present in the fields. As soon as the crop is off 
the remnants should be gathered and burned. All weeds in the vicinity 
should be kept down thruout the year, including late fall and early 
spring, since, as has already been shown, the common weeds of the 
field and garden are available as alternate 
food plants and serve as the hibernating 
quarters of the aphides, which feed more or 
less thruout the warmer periods of winter. 

On weeds the insects can be found feeding, III ^^^^^ '«-. 

in a climate like that of the District of 
Columbia, untilJanuar}^, ''even after heavy 
frosts or snow," and again in March. 

CONTROL OF THE MELON APHIS BY NATURAL 
ENEMIES. 

The possible control of this pest with 
the assistance of its natural enemies, aided 
by a trap crop, 
is proposed by 
Mr. Sanborn, who 
has placed at the 
writer's disposal 
advance sheets of 
his publication in 
which this method 
is described. 

Rape, which is of 
value for hog and 
sheep pasture, is 
the crop advised. 
Kale or mustard" 
should serve the 
same purpose. This method begins in the fall when the trap crop is 
planted. 

The cabbage aphis {Aphis brassicse L.) is closely related to, but 
quite distinct from, the melon aphis. It winters over on the trap 

^'For several years the writer has observed that these two crops serve as a trap 
for the cabbage aphis, by luring them from cabbage and more valuable crops; also, 
that they are here largely destroyed and practically held in check by their principal 
insect enemies — which have been illustrated in figure 3; and the idea of employing 
this means of attracting the natural enemies was suggested to the writer in 1900. 




Fig. 6.— Knapsack sprayer in operation, showing method of applying 
nnderspray. 



16 

crop and attacks it earh' in spring, when, unless the natural enemies 
come to the fore, it niultiplies in great abundance. In the writers 
experience the lad3'birds and other enemies soon gain the ascendancy 
and become so abundant that the}^ are forced to migrate for food. 
The trap crop will ordinarih^ remain in condition to sustain aphides 
and their enemies until melons or other crops susceptible to melon- 
aphis damage have past the danger stage and are ripening. 

The farmer may exercise his own judgment in regard to the loca- 
tion of the trap crop. The writer believes that the greatest advantage 
would accrue from planting three or more rows of rape or kale on 
each side and, in the case of lields of more than 4 or 5 acres, bv plant- 
ing additional rows between. Planted on all sides, the trap crop will 
attract aphides and their enemies from every direction, and this result 
will be facilitated b}^ permitting the growth of weeds between the 
rows. In fact, weeds are a desideratum in these operations, since 
they furnish the best natural hibernating places for the lad3^birds and 
similar beneficial insects. It is advisable also to place boards, loose 
bark, or hollow logs about the margins of the fields to secure better 
facilities for hibernation. As fast as one crop of rape, or whatever 
is used, matures, or its growth is stopt by the aphides (as might 
sometimes happen), another planting should be made so as to keep a 
constant suppl}^ of cabbage aphides on hand that the natural enemies 
may not migrate to other quarters. 

COXCLUSIOX. 

Many of the remedies that have been indicated as of service in the 
control .of the melon aphis (with the exception of the last) operate 
against most other cucurbit insects, several species of which are 
usually present. Thus the kerosene emulsion and soap solutions kill 
young squash bugs and act as deterrents to most other insects, and 
bisulfid of carbon will kill other soft-bodied insects besides the aphides, 
while fall plowing and clean cultural methods are valuable in destroy- 
ing the squash-vine borer. Tobacco fumigation, however, has little 
effect on these other insects as they occur in the fiekL 

Approved: 

James Wilson, 

Secretary of Agriculture^ 

Washington, D. C, Novemher IJ^, 1906. 

O